Injection Blow Molding (IBM) is well known as a manufacturing process for making hollow plastic parts. Typically, small plastic pellets or granules are melted into a liquid, the molten liquid passed through a nozzle, and then formed into a parison or hollow tube in a parison cavity. The parison is then transferred to a blow mold consisting of two clamped mold halves where the parison is inflated until it expands to fill the shape of the mold. The mold halves are then unclamped and the blow molded piece is removed.
One important consideration in an IBM system is ensuring that the centerline of the injector nozzle that injects the molten plastic and the centerline of parison cavity that receives the molten plastic are aligned. Numerous conditions cause the misalignment of these centerlines. For example, because the parison cavity and the nozzle are often operating at drastically different temperatures (sometimes as high as a 300 degree F. difference), the nozzle and parison cavity are often expanding at different rates and therefore their centerlines are moving at different rates thus causing misalignment. That temperature difference between the injector nozzle tip and the parison cavity also causes the nozzle tip to cool slightly and solidify plastic prematurely.
Thus, conventionally, the parison cavity is at one temperature and the injector nozzle is at another, cooler, temperature and therefore different thermal expansions cause the plastic material to leak out of the cavity and create a pool of liquid between the parison cavity block and the injector nozzle.
Not only does the temperature difference create a misalignment of the centerlines but also the actual alignment and assembly of the nozzle to the parison cavity can create a misalignment. In other words, the actual construction of the system in mounting the injector nozzle to the parison cavity is not sufficiently rigid and robust and a misalignment of the centerlines can occur. It is difficult to mount the injector nozzle and the parison cavity in the proper orientation in a robust manner that ensures the proper alignment of the respective axes.
Misalignment of the nozzle and parison cavity centerlines is disadvantageous for a variety of reasons. For example, misalignment causes leakage to occur between the nozzle and the parison cavity. Leakage of the molten plastic can cause machine stoppage (thus stopping production) and even machine destruction. Further, excessive nozzle replacement also occurs when there is excessive leakage. Misalignment of the centerlines also results in inconsistent cavity balance and fill rates. Cavity balance and fill rates are important in producing products of exacting specifications. Stated differently, inconsistent cavity balance and fill rates lead to molded pieces with varying weight and cosmetics leading to molded pieces that are not made to specification. In sum, misalignment of the centerlines costs time and money.
Accordingly, it would be advantageous to provide an IBM system and method of using the system that reduces the temperature differential between the injector nozzle and the parison cavity to better assure that the centerline of the injector nozzle and the parison cavity is maintained in light of thermal expansion and other variables. In addition, it would be advantageous to provide a means of mounting the injector nozzle to the parison cavity in a manner that the alignment of the centerline of the injector nozzle and the parison cavity is assured.